1. Field of the Invention
The present invention relates to a toner for use in, for example, an image forming method and a toner jet method each intended for visualizing an electrophotograph, that is, an electrostatic charge image.
2. Description of the Related Art
A large number of image forming methods such as electrophotographic methods, that is, electrostatic recording methods, magnetic recording methods, and toner jet methods have been conventionally known. For example, such methods as described in U.S. Pat. No. 2,297,691, JP 42-23910 B, and JP 43-24748 B have been known as electrophotographic methods. A general electrophotographic method involves: utilizing a photoconductive substance; forming an electrostatic latent image on a photosensitive member by using various means; developing the latent image with toner to provide a visible image; transferring the toner onto a transfer material such as paper as required; and fixing the toner image onto the transfer material by using heat, pressure, or the like to provide a copied article. The toner remaining on the photosensitive member without being transferred is cleaned by means of various methods, and then the above steps are repeated.
In recent years, reductions in size and weight of a copying device for use in such electrophotographic method and improvements in speed and reliability (such as high definition or high image quality) of the device have been stringently pursued. For example, the copying device, which has been heretofore used as a copying machine for use in paper work for copying a mere original manuscript, starts to be used as a digital printer serving as the output of a computer or as a printer for copying a highly fine image such as a graphic design, and to be used for light printing where improved reliability is requested (a print-on-demand application where many kinds can be printed each in a small amount, the application ranging from the editing of a document by using a personal computer to the copying and binding of the document). Accordingly, improved image quality including improved definition has been requested. As a result, performance requested for toner has become more and more sophisticated.
Conventionally, each of a polyester unit and a vinyl copolymer unit such as a styrene resin has been mainly used as a resin for toner. The polyester unit originally has excellent low-temperature fixability, but involves a disadvantage in that an offset phenomenon at a high temperature is liable to occur. When one attempts to increase the molecular weight of the polyester unit to increase a viscosity in compensation for the disadvantage, low-temperature fixability is impaired, and grindability upon toner production degrades. Accordingly, the increase does not qualify for a reduction in particle size of toner.
In addition, the vinyl copolymer unit such as a styrene resin is excellent in grindability upon toner production, and is excellent in hot offset resistance because the molecular weight of the unit can be easily increased. However, a reduction in molecular weight of the unit with a view to improving low-temperature fixability degrades blocking resistance and developability.
A possible way to compensate for the disadvantages of those two kinds of resins while making effective use of the advantages of the resins relates to use the polyester unit and the vinyl copolymer unit as a mixture. However, mere mixing of them provides toner having a narrow fixation region because compatibility between them is insufficient. Moreover, the mixing degrades blocking resistance and developability.
JP 11-194536 A and JP 2000-56511 A each disclose a toner using at least two kinds of resins out of a polyester resin, a styrene resin, and a resin obtained as a result of a reaction between part of a styrene resin and a polyester resin. In each of those methods, compatibility between the polyester resin and the styrene resin improves, and toner having a wide fixation temperature region can be obtained. However, the performance of the toner is not yet sufficient in a machine that has realized a fixation method requested in recent years with which copying can be performed at a high speed and a low power consumption. That is, an increase in copying speed shortens a time period for which a recording material passes through a fixing unit even when a heating temperature or applied pressure upon fixation is comparable to a conventional one. In other words, the total quantity of heat (work done) to be applied to the recording material is liable to reduce, so an additional improvement in fixability of toner is indispensable.
Furthermore, JP 2001-13720 A discusses the properties of a polymer that does not affect fixation through the specification of a difference between the amount of soluble matter and the amount of insoluble matter in each of different solvents with regard to a toner component, as a result, discloses a technique for producing toner with which a wide fixation region can be obtained. Although the method can provide a resin design that hardly inhibits fixability, a wait time is short. Accordingly, the resin design must be additionally improved so that a fixation method requiring a low power consumption is realized.